Author Topic: Scanner/Multiplexers for voltage references  (Read 6279 times)

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Offline Kleinstein

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Re: Scanner/Multiplexers for voltage references
« Reply #50 on: June 16, 2021, 03:59:37 pm »
This is an interesting construction to get low thermal EMF reed relais.

The contact block does not look that impressive: I kind of miss more area to thermally couple the incoming wires to the metal block.
 

Offline Andreas

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Re: Scanner/Multiplexers for voltage references
« Reply #51 on: June 16, 2021, 07:17:47 pm »
Hello,

the effort is absolutely necessary.

The wires through glass are most probably out of Covar with a high thermal EMF against copper.
And the wires are not closely neighboured.

with best regards

Andreas
 

Online dietert1

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Re: Scanner/Multiplexers for voltage references
« Reply #52 on: June 26, 2021, 08:59:44 pm »
Meanwhile i started using the low thermal scanner i described above, with two 3457A meters connected to the output. I am monitoring one of the 10 V references in 30 V range and voltage differences in 10 mV range. Today i found that avoiding transient overvoltage to the meter can make a difference. This means:
- not using autorange
- setting the meter for a higher voltage range before switching the MUX
- switching the MUX before setting the meter for a lower voltage range

When measuring 10 V the average TC of the two meters is about 0.6 ppm/K. One thing i still need to study is the guard of the HP 3457A. It does have a cage around the floating part but no separate guard terminal. Maybe i can disconnect the cage from the low terminal and add a guard terminal.

Regards, Dieter

 
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